Depolymerization of recovered plastic materials

Abstract

Described herein are systems and methods for the depolymerization of polyethylene-based plastics. In one embodiment, a method is disclosed that comprises combining a polyethylene-based plastic with a solvent in a reactor to generate a plastic solvent mixture, heating the plastic solvent mixture in the reactor, and fractionating the plastic solvent mixture into a gas phase product, a solid phase product, and a liquid phase product. In another embodiment, a system is disclosed that comprises a solvent, and a reactor configured to receive the polyethylene-based plastic and the solvent and convert the polyethylene-based plastic into a gas phase product, a solid phase product, and a liquid phase product, the reactor being configured to operate at a temperature greater than 275° C. and at a pressure greater than 2 megapascals.

What is claimed is: 
     
       1. A method for depolymerizing a polyethylene-based plastic, the method comprising:
 combining the polyethylene-based plastic with a solvent in a reactor to generate a plastic solvent mixture; 
 heating the plastic solvent mixture in the reactor at a temperature no greater than 360° C. for no less than 70 minutes and no greater than 120 minutes; and 
 fractionating the plastic solvent mixture into a gas phase product, a solid phase product, and a liquid phase product wherein the plastic solvent mixture is further combined with an ionic liquid catalyst prior to heating with. 
 
     
     
       2. The method according to  claim 1 , wherein the solvent comprises at least one of water, methanol, ethanol, butanol, isopropyl alcohol, or acetone. 
     
     
       3. The method according to  claim 2 , wherein the solvent comprises acetone. 
     
     
       4. The method according to  claim 1 , wherein the ionic liquid catalyst comprises 1-butyl-3-methylimidazolium, bis[(perfluoroethyl)sulfonyl]-imide ([BMIM][PF2]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), or combinations thereof. 
     
     
       5. The method according to  claim 1 , wherein the heating is performed at about 300° C. to 360° C. 
     
     
       6. The method according to  claim 5 , wherein the heating is performed between about 340° C. to 360° C. 
     
     
       7. The method according to  claim 1 , wherein the heating is performed at a pressure of about 2 megapascals to about 20 megapascals. 
     
     
       8. The method according to  claim 7 , wherein the heating is performed at a pressure of about 8 megapascals to about 11 megapascals. 
     
     
       9. The method according to  claim 1 , wherein the heating is performed for about 80 minutes to about 100 minutes. 
     
     
       10. The method according to  claim 1 , wherein the plastic solvent mixture is combined in a weight/volume ratio of about 1 gram plastic:6 mL solvent to about 1 gram plastic:20 mL solvent. 
     
     
       11. The method according to  claim 1 , further comprising separating the gas phase product and the liquid phase product using a combined membrane and adsorption process. 
     
     
       12. The method according to  claim 1 , wherein at least 60% of the polyethylene-based plastic is converted into the gas phase product and the liquid phase product. 
     
     
       13. The method according to  claim 1 , wherein at least 30% of the polyethylene-based plastic is converted into the liquid phase product. 
     
     
       14. The method according to  claim 1 , wherein the liquid phase product has an oxygen/carbon ratio of about 0.01 to about 0.70. 
     
     
       15. The method according to  claim 1 , wherein the liquid phase product has a hydrogen/carbon ratio of about 1.4 to about 2.0. 
     
     
       16. The method according to  claim 1 , wherein the liquid phase product has a high heat value of about 35 MJ/kg to about 45 MJ/kg. 
     
     
       17. A method for depolymerizing a polyethylene-based plastic, the method comprising:
 combining the polyethylene-based plastic with a solvent comprising acetone in a reactor to generate a plastic solvent mixture; 
 heating the plastic solvent mixture in the reactor at a temperature no greater than 360° C., at a pressure greater than 2 megapascals, and for no less than 70 minutes and no greater than 120 minutes; 
 fractionating the plastic solvent mixture into a gas phase product, a solid phase product, and a liquid phase product; and 
 
       separating the gas phase product and the liquid phase product using a combined membrane and adsorption process. 
     
     
       18. A method for depolymerizing a polyethylene-based plastic, the method comprising:
 combining the polyethylene-based plastic with a solvent comprising acetone in a reactor to generate a plastic solvent mixture; 
 heating the plastic solvent mixture in the reactor at a temperature no greater than 360° C. for no less than 70 minutes and no greater than 120 minutes; and 
 fractionating the plastic solvent mixture into a gas phase product, a solid phase product, and a liquid phase product.